128 research outputs found
High-energy cryogenic Yb amplifiers and their applications to nonlinear post-compression and tunable wavelength shifting
No full textScaling of peak and average power in femtosecond ytterbium amplifiers
No full textScaling of output parameters of femtosecond laser systems is one of the highly demanded and challenging tasks in modern laser science and engineering. Fundamental science requires ever shorter pulses and higher pulse energies for investigation of ultrafast processes taking place in matter and for new discoveries in the area of strong field physics. Achievable laser intensity has rapidly grown over recent decades with such milestone inventions as chirped pulse amplification (CPA) and implementation of new broadband solid-state laser gain media. Next to fundamental science, laser machining and material processing see increasing adoption in various industries, and benefit from high repetition rate and average power of lasers. Advent of diode-pumped solid-state (DPSS) Yb3+-doped laser technology brought a breakthrough in quantum efficiency and obtainable average power. The efficiency can be further improved by utilizing cryogenic cooling of the gain medium,as it reduces ground state abosption (GSA), considerably improves thermal conductivity and boosts gain and absorption cross-sections of the gain medium. This work is dedicated to peak and average power scaling of cryogenically cooled DPSS Yb3+:CaF2 femtosecond CPA system. Firstly, it aims at upscaling of both peak and average power of a regenerative amplifier (RA) via innovative design of the RA cavity, in particular, by employing a cavity with a dual gain medium and by increasing the mode size on the optical elements. In-depth analysis of the design and experimental verification will be given by considering cavity stability, thermal lensing and thermal management, laser crystal geometry, accumulated nonlinear phase (B-integral), suppression of bifurcations of pulse energy and spectral gain narrowing. Developed CPA system operating at central wavelength of 1030 nm and generating 220-fs pulses with energies exceeding 30 mJ will be presented. The system is capable of delivering up to 24 W of average power at 10-kHz repetition rate. Further upscaling of the peak power to TW-level is achieved by implementing a multipass amplifier (MPA) booster stage after the RA. Here, challenges that are specific to multipass amplifiers (as compared to RAs) will be considered, e.g. compensation of astigmatic aberration and spatial gain narrowing, mitigation of self-phase modulation (SPM) and amplified spontaneous emission (ASE), preservation of the beam quality via repetitive imaging. Other crucial design parameters, such as laser crystal geometry and cooling, pump beamline arrangement, thermal lensing and B-integral will be also discussed. A multistage CPA system producing120-mJ, 225-fs pulses at a repetition rate of 50 Hz with the beam quality parameter M2 less than 1.1 will be introduced. Finally, a nonlinear pulse compression is applied by means of spectral broadening and shifting of the generated 220-fs pulses via cascaded stimulated Raman scattering (SRS) process in a N2-filled stretched hollow core fiber (HCF) and subsequent compression in a set of chirped mirrors. As a result, 14-mJ, 20-fs pulses are obtained, with the central wavelength shifted from 1.03 μm to 1.3 μm, which is crucial for the high harmonic generation (HHG) in the carbon K-edge spectral region
Numerische und experimentelle Charakterisierung eines kryogen-gekühlten mehrgängigen Yb:CaF2 Laser-Verstärkers
No full textPresent thesis is dedicated to study and realization of cryogenically cooled solid-state multi-pass (MP) Yb3+:CaF2 laser amplifier. Within the scope of the thesis specific design questions as active medium choice, thermal behavior of the amplifier, pumping setup, as well as experimental results of the measurements of the amplifier performance will be considered. We have implemented MP scheme seeded by regenerative preamplifier stage and pumped with InGaAs diode laser stack, which can produce up to 200 W average power of pump radiation. Regenerative amplifier, developed during past years in Ultrafast Laser Group at Photonics Institute [Pugzlys, 2009] is capable of delivering up to 10 mJ energy in 500 ps broadband pulses with ~12 nm bandwidth at FWHM. In the framework of this work we aimed to reach 100 mJ output pulse energy at 100 Hz frequency. We provide extensive characterization of implemented MP amplifier, which includes small-signal gain measurement, output energy measurements, output pulse cross-section and spectrum measurements. We address the challenge of beam narrowing during amplification process and offer a solution to resolve it. Achievement of 100 mJ output pulse energy with spectral band of ~12 nm at FWHM at 50 Hz repetition rate is confirmed. We conduct numerical modelling of heat dissipation in the Yb:CaF2 crystal thermally bonded with blank CaF2 slabs. Thermal behavior of bonded structure is studied in dependence on the thickness of undoped regions and active area. Heat distribution in the case of double-sided pump is compared to the case of single-sided pump
Rapid-scan nonlinear time-resolved spectroscopy over arbitrary delay intervals
No full textFemtosecond dual-comb lasers have revolutionized linear Fourier-domain
spectroscopy by offering a rapid motion-free, precise and accurate measurement
mode with easy registration of the combs beat note in the RF domain. Extensions
of this technique found already application for nonlinear time-resolved
spectroscopy within the energy limit available from sources operating at the
full oscillator repetition rate. Here, we present a technique based on time
filtering of femtosecond frequency combs by pulse gating in a laser amplifier.
This gives the required boost to the pulse energy and provides the flexibility
to engineer pairs of arbitrarily delayed wavelength-tunable pulses for
pump-probe techniques. Using a dual-channel millijoule amplifier, we
demonstrate programmable generation of both extremely short, fs, and extremely
long (>ns) interpulse delays. A predetermined arbitrarily chosen interpulse
delay can be directly realized in each successive amplifier shot, eliminating
the massive waiting time required to alter the delay setting by means of an
optomechanical line or an asynchronous scan of two free-running oscillators. We
confirm the versatility of this delay generation method by measuring chi^(2)
cross-correlation and chi^(3) multicomponent population recovery kinetics
Suppression of Kerr-induced satellites in multi-pulse CPA
No full textAmplification of bursts of ultrashort pulses is very challenging when the intraburst repetition frequency reaches the THz range, corresponding to (sub)-ps intervals between consecutive pulses. Periodic interference significantly modifies conditions for chirped pulse amplification (CPA), leading to temporal and spectral distortions during CPA due to optical Kerr nonlinearity. Multi-pulse chirped amplification to mJ energies may lead to a pronounced degradation of burst fidelity and the appearance of periodic temporal satellites after de-chirping the amplified waveform. We study, experimentally and numerically, the limitations of THz burst-mode CPA caused by self- and cross-phase modulation. A number of practical recipes to suppress nonlinear distortions and improve energy scaling by optimizing burst parameters and applying modulation techniques are presented
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